The present invention relates to direct current detection circuits, and in particular to an off-hook detector circuit for a telephone line.
With telephone equipment, it is frequently necessary to determine when the telephone has been taken off-hook. For example, in a party telephone line, it may be necessary to provide an automatic number identifying mark on the telephone line when a particular telephone instrument has gone off-hook so that the particular party on the party line may be properly identified at the telephone central office for billing purposes.
At the same time, it is important that an off-hook detector circuit for use with telephone equipment not be affected by other signals on the telephone line, for example ringing and noise signals.